Glucagon-like peptide-2 (GLP-2) is a 33-amino acid proglucagon-derived peptide secreted by the endocrine L-cell primarily in the lower gastrointestinal tract in response to luminal nutrients. Plasma levels have been shown to significantly increase within an hour of ingesting a meal, in particular following the ingestion of carbohydrates or fat (1). GLP-2 has been shown to be responsible for the regulation of proliferation and apoptosis of the intestinal epithelium (2,3). These changes in part result in an increase in mucosal surface area, enhanced absorptive efficiency and barrier function in the small intestine (4-6). GLP-2 also decreases gastric motility, inhibits gastric acid secretion, increases nutrient transport activity and acutely increases intestinal and portal blood flow (7-11).
GLP-2 and GLP-2 analogues promote the growth and repair of the intestinal epithelium in models of disease, including enhanced adaptation and nutrient absorption following small bowel resection and alleviation of TPN-induced hypoplasia in rodents (12-15). GLP-2 analogues have demonstrated decreased mortality and improvement of disease-related histopathology in animal models of intestinal damage such as indomethacin-induced enteritis, dextran sulfate-induced colitis and chemotherapy-induced mucositis (16-19).
The intestinotrophic effects of GLP-2 are mediated by the GLP-2 receptor (GLP-2R), a member of the superfamily of G-protein coupled receptors and most closely related to the GLP-1 and glucagon receptor gene subfamily (20). The GLP-2R is a high-affinity, ligand-specific functional receptor coupled to the G-protein Gs. Studies of the activation of the cloned GLP-2R by GLP-2 analogues show a correlation of in vitro activity with in vivo intestinotrophic efficacy (20).
To date, characterization of GLP-2R function has been limited to heterologous cell line expression, mucosal fractions and primary cell cultures. GLP-2 selectively stimulates cAMP production in recombinantly expressing GLP-2R cell lines, isolated intestinal mucosal fractions containing enteroendocrine and neural cells and primary hippocampal cultures (21-24). The study of native GLP-2R biological activity has focused on in vivo animal models and ex vivo model systems that require exogenous application of GLP-2 to the whole animal prior to tissue isolation (2-19, 25-31). There is no ex vivo method for characterizing putative GLP-2 ligands directly; such a method would have obvious utility, for example in the screening and characterization of GLP-2 ligands of pharmaceutical interest.